A network device having a so-called content-filtering function has conventionally been developed, in which network device it is possible to restrict access, of a communication terminal connected to a LAN (local area network), to a particular server or content on an external network such as the Internet (see, for example, Patent Literature 1).
The following description deals with an example arrangement of a conventional content-filtering system with reference to FIG. 15. FIG. 15 is a functional block diagram schematically illustrating an arrangement of a conventional content-filtering system 20.
As illustrated in FIG. 15, a content-filtering device 500 is provided between a communication connection device 400 and the Internet 300. Communication terminals T1 through Tn are connected to ports P1 through Pn of the communication connection device 400, respectively.
A request to be transmitted from any of the communication terminals T1 through Tn to a web server (not shown) on the Internet 300 is first transmitted, via a communication connection section 410 of the communication connection device 400, from a LAN interface 430 to the content-filtering device 500.
In the content-filtering device 500, the request is received at a LAN interface 530, and a content-filtering performing section 520 performs verification for the request by referring to a content filter DB 510. If the request is verified, the request is transmitted from a WAN interface 540 to the Internet 300.
Examples of the filtering function encompass: a filtering function which restricts access to a particular domain or URI (uniform resource identifier); a filtering function which restricts access in accordance with what kind of content is to be accessed and/or what is contained in the content; and a filtering function which, for example, modifies the content itself so that it is appropriate (see, for example, Patent Literature 2). Examples of the network device encompass a router, a proxy server, etc.
A network device having the above filtering function has been introduced in, e.g., an in-house network of a company so as to, for example, (i) prohibit or restrict viewing of content unnecessary for work and/or (ii) prevent a network band from being congested due to careless access to content. Since access to large-volume content such as moving image data and audio data tends to occupy a large portion of the network band, access to such content is in particular restricted in some companies.
As another technique related to the network device, a switching hub has been developed which can switch its transmission rate stepwise by switching its operation modes. The operation modes are settings as to a transmission rate and a transmission mode. The transmission rate is set stepwise. Examples of the transmission mode encompass a full-duplex transmission, a half-duplex transmission, etc.
The switching hub may have an auto-negotiation function, by which an adjustment is made so that the switching hub can operate normally at the highest transmission rate if possible or in a high-priority operation mode.
Further, a proposal has been made in which ports of a switching hub are monitored so that the changing an operation mode to an operation mode having a lower transmission rate for the ports being monitored is carried out such that a port having the lowest line utilization is preferentially changed (see, for example, Patent Literature 3).
Patent Literature 3, for example, discloses a technique in which a transmission rate is changed by switching from an operation mode having a 100-Mbps (megabits per second) full-duplex transmission to an operation mode having a 10-Mbps full-duplex transmission.
As described above, a switching hub may be capable of switching between (i) an operation mode having a high transmission rate which is sufficient to transmit or receive large-volume content data and (ii) an operation mode having a low transmission rate which is sufficient to transmit or receive small-volume content data (e.g., text-based data such as email).